Electrical systems



April 20, 1965 c. B. HENMAN 3,179,876

ELECTRICAL SYSTEMS Filed Sept. 6, 1960 3,179,876 ELECTRICAL SYSTEMSCecil Bourne Hellman, Ifield, Crawley, England, assignor to BrentfordTransformers Limited, Crawley, England Filed Sept. 6, 1969, Ser. No.54,058

Claims priority, application Great Britain, Apr. 5, 1960,

6 Claims. (Cl. 323-45) The present invention concerns improvements in orrelating to electrical systems."

Electrical systems (as the term is used in this specification) are usedfor the purpose of changing or controlling the voltage as between aninput and an output and it is known that in such electrical systemsvoltage changing devices such as single-wound transformers,auto-transformers, regulators, double-wound transformers, and the likeare all used for the purpose of changing or controlling the voltage.These electrical control devices are of two main types, namely the typein which a stepwise control of the voltage is achieved and the type inwhich a substantially smooth control of the voltage is achieved. Some ofthese voltage changing devices are provided with contacts or other formof tapping points and in the case of those having contacts, the contactsmay be designed for movement when either on-load or ofi-load.

According to the present invention there is provided an electricalsystem comprising a voltage control device having means to deliver twovoltages which are oppositely changeable in synchronisrn, in combinationwith a static transformer having at least two windings fed respectivelyby the two voltages and the output voltage of the system being developedin association with the static transformer windings.

In one arrangement the static transformer has the two windings acting asprimary windings and is provided with a secondary winding from which theoutput voltage is derived but in another arrangement one of the windingsacts as an auto-winding and the output voltage is taken from thiswinding.

In order that the invention may more readily be understood certainembodiments of the same will now be described by way of example and withreference to the accomp anying drawings, wherein- FIGURE 1 shows asimple embodiment showing a double-wound static transformer,

FIGURE 2 shows an auto-Wound static transformer, and

FEGURE 3 shows a modification of FIGURE 2.

Referring now to FIGURE 1, it will be seen that the electrical system ofthis invention comprises voltage control device VCD which is connectedacross live and neutral supply lines L and N respectively. This voltagecontrol device may be of any form such as a tapped transformer orvoltage regulator but is illustrated in a manner suitable for a voltageregulator of the type in which a pair of contacts track opposite sidesof a straight coil these two contacts being interconnected by a chain orthe like. Thus the contacts C1 and C2 deliver two voltages which areoppositely changeable in synchronism. This voltage control, device VCDis connected in combination with a static transformer ST having twoprimary windings P1 and P2 and a single secondary winding S. The Voltagefrom the contact C1 is fed to the primary winding P1, the other end ofwhich is connected to the neutral supply line N, whilst the voltage fromthe contact C2. is fed to the primary winding P2 and the other end ofthis primary winding is connected to the live supply line L. Thesecondary winding S develops an output voltage which is delivered fromterminals 01 and 02.

In the conventional arrangement the circuit would be United StatesPatent O 3,179,876 Patented Apr. 20, 1965 that of FIGURE 1 except thatthe primary winding P2 and contact C2 would be omitted. V In such anarrangement and assuming a 400 volt supply, a regulator VCD capableofcarrying a maximum 100 amps would be necessary to achieve 0 to 40 kva.variation. However, with the circuit of FIGURE 1 and in order to achievethe same variation, the current carrying capacity of the regulator needonly be 50 amps maximum. Clearly the current carrying capacities of thetransformer windings and contacts will suit the regulator currentcarrying 7 capacity.

FIGURE 2 shows the'circuit arranged for auto-connection in a parallelarrangement and, referring to FIGURE 2, the supply linesL-and N areagain connected to a voltage control device VCD which has contacts C1and C2 in the same arrangement as in FIGURE 1. The contact C2 isconnected to a primary winding P of the static transformer ST, the otherend of this primary winding being connected to the live supply line L.The static transformer ST has a secondary winding S which has one endconnected tozthe neutral supply line N and the other end connected tothe contact C1. via a balancer winding B. The output is developedbetween the neutral supply line N and a centre tap on the balancerwinding B which is connected to an output contact 0.

In this arrangement it will be clear that the input and output lines arenot isolated from one another, since the neutral line N is common toboth, but nevertheless the voltage developed across the output lines 0and N may be varied between 0 and 400 volts at a power rating of 40 kva.when the power ratings of the regulator VCD and the two transformerwindings are 20 kva. This arrangement gives the same degree'ofregulation as that of a single 40 kva. regulator and it is estimatedthat the cost of a 20 kva. regulator is only approximately half that ofa 40 kva. regulator and is moreover approximately half the size.

FIGURE 3 shows the parts connected for auto-series operation and onceagain the regulator VCD is connected across the live and neutral supplylines L, N. Once again also the contact C2 is connected to the primarywinding P of the transformer ST and thence to the live supply line butthe contact C1 is connected to the secondary winding S of thetransformer ST, the other end of this secondary winding being connecteddirectly to the output point 0.

While I have shown and described what I believe to be the bestembodiments of my invention, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

I claim:

1. In a voltage control system comprising a voltage dividing element; apair of contacts movable over said voltage dividing element in oppositedirections in synchronism; and a transformer having a plurality ofwindings including a first winding and a second winding, the firstwinding being connected between one of said contacts and one electricalend of the voltage dividing element and the second winding beingconnected between the other of said contacts and the other electricalend of the voltage dividing element.

2. A voltage control system according to claim 1 fur ther comprising athird winding on said transformer insulated from said first and secondwindings, the controlled voltage being developed in said third winding.

3. A voltage control system comprising: a pair of input terminals; apair of output terminals; an auto-transformer having a winding connectedfor energization from said input terminals; a pair of contact means eachmovable u electrically with respect to said windingv for adjustablyselecting different voltages therefrom, said contact means beingconstrained to move simultaneously in opposite directions toward andaway from the electrical center of said winding to select a decreased oran increased voltage, respectively, from said winding; and circuit meansincluding a transformer having two separate windings, said windingshaving equal numbers of turns, one of said separate windings beingconnected between one of said contact means and one of said terminals,the other of said separate windings being connected between the other ofsaid contact means and another one of said terminals to produce voltagesin both windings which are in phase with each other and which increaseprogressively as said contact means are moved away from said electricalcenter of said winding of said auto-transformer, and further circuitmeans connected to deliver the combined voltages of said separatewindings to said output terminals.

4. A voltage control system according to claim 3, further comprising abalancing circuit element included in said further circuit means, saidcircuit element being connected to one of said output terminals and oneof said separate transformer windings for obtaining said balancedrelationship.

5. A voltage control device comprising an auto-transformer windinghaving a first and a second electrical end, a first and a secondconnection means for making adjustable connections to theauto-transformer winding, and a multi-winding transformer having twoprimary windings and a secondary winding, one primary winding beingconnected between one electrical end and the first connection means, theother primary winding being connected between the other electrical endand the second connection means, the primary windings having the samenumber of turns, the first and second connection means being so arrangedthat equal voltages are applied to the primary windings, and the primarywindings inducing voltages of the same phase in the secondary winding.

6. A voltage control system according to claim 3, wherein said separatewindings are connected each between one of said contact means and one ofsaid input terminals, and in which said transformer further comprises aseparate third winding connected to said output terminals.

References Qited by the Examiner UNITED STATES PATENTS 5/34 Blume 323-8/43 Blume 32345 ORIS L. RADER, MILTON O. HIRSHFIELD,

Examiners.

1. IN A VOLTAGE CONTROL SYSTEM COMPRISING A VOLTAGE DIVIDING ELEMENT; APAIR OF CONTACTS MOVABLE OVER SAID VOLTAGE DIVIDING ELEMENTS IN OPPOSITEDIRECTIONS IN SYNCHRONISM; AND A TRANSFORMER HAVING A PLURALITY OFWINDINGS INCLUDING A FIRST WINDING AND A SECOND WINDING, THE FIRSTWINDING BEING CONNECTED BETWEEN ONE OF SAID CONTACTS AND ONE ELECTRICALEND OF THE VOLTAGE DIVIDING ELEMENT AND THE SECOND WINDING BEINGCONNECTED BETWEEN THE OTHER OF SAID CONTACTS AND THE OTHER ELECTRICALEND OF THE VOLTAGE DIVIDING ELEMENT.